We are utilizing thymidine kinase minus mammalian cells to study the details of mitochondrial DNA replication and function. These cells incorporate thymidine and thymidine analogues into mitochondrial DNA. We are also studying the effects of chemotherapeutic drugs known to inhibit DNA synthesis. BIBLIOGRAPHIC REFERENCE: Clayton, D.A. and C.A. Smith, Complex Mitochondrial DNA, Int. Rev. of Exp. Path. 14:1 (1975).